<?php
/*
 *  $Id$
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * This software consists of voluntary contributions made by many individuals
 * and is licensed under the LGPL. For more information, see
 * <http://www.doctrine-project.org>.
 */

namespace Doctrine\Common;

/**
 * EventArgs is the base class for classes containing event data.
 *
 * This class contains no event data. It is used by events that do not pass state
 * information to an event handler when an event is raised. The single empty EventArgs
 * instance can be obtained through {@link getEmptyInstance}.
 *
 * @license http://www.opensource.org/licenses/lgpl-license.php LGPL
 * @link    www.doctrine-project.org
 * @since   2.0
 * @version $Revision: 3938 $
 * @author  Guilherme Blanco <guilhermeblanco@hotmail.com>
 * @author  Jonathan Wage <jonwage@gmail.com>
 * @author  Roman Borschel <roman@code-factory.org>
 */
class EventArgs {
	/**
	 * @var EventArgs Single instance of EventArgs
	 * @static
	 */
	private static $_emptyEventArgsInstance;
	
	/**
	 * Gets the single, empty and immutable EventArgs instance.
	 *
	 * This instance will be used when events are dispatched without any parameter,
	 * like this: EventManager::dispatchEvent('eventname');
	 *
	 * The benefit from this is that only one empty instance is instantiated and shared
	 * (otherwise there would be instances for every dispatched in the abovementioned form)
	 *
	 * @see EventManager::dispatchEvent
	 * @link http://msdn.microsoft.com/en-us/library/system.eventargs.aspx
	 * @static
	 * @return EventArgs
	 */
	public static function getEmptyInstance() {
		if( !self::$_emptyEventArgsInstance ) {
			self::$_emptyEventArgsInstance = new EventArgs();
		}
		
		return self::$_emptyEventArgsInstance;
	}
}
